This invention relates to improvements in a porcelain-clad electrical machine with a vibration-on-transportation suppression.
A conventional one of porcelain-clad electrical machine of the type referred to has comprised an upper tank, a lower tank, a hollow porcelain tube connected at both ends to the upper and lower tanks through respective packings, an electrical machine such as a transformer fixed between a pair of electrically insulating plates extending through the interior of the porcelain tube, and a compression controlled helical spring disposed in the upper tank to controllably tension an associated one of the electrically insulating plates with respect to the lower tank.
In the arrangement as described above each of the helical springs has been compressed by an associated fastening nut to cause a tensioning force on the associated electrically insulating plate. Then a reaction of the tensioning force imparts surface pressure to the packings on both ends of the porcelain tube to hold a relative positional relationship among the components involved as required.
Upon the transportation thereof, the porcelain-clad electrical machine such as described above may be applied with excessive vibrations which are generally in excess of five to ten times vibrations developed upon the installation. In order to ensure that the electrical machines have the resistance to such excessive vibrations, there is nothing for it but to increase a clamping force of the helical spring. This is because the surface pressures applied to the packings originate only from the clamping force of the helical springs. When the increase in clamping force lacks in the safety of the procelain-clad electrical machine, the porcelain tube has been provided on the inner wall of that end thereof adjacent to the lower tank with a center rest.
Those measures, however, have caused the electrically insulating plates and the associated components to be large as an increase in claimping force of the helical spring resulting in the necessity of rendering the porcelain tube, the tanks etc. large-scaled. Accordingly the cost of transportation has tended to be expensive.
Also the higher the clamping force of the helical spring the more the workability of compressing the helical spring will be deteriorated upon the compression thereof.
Furthermore with the center rest disposed on the inside of the procelain tube, the latter has been required to increase in dimensional tolerance of the inside diameter thereof. Therefore a cushion should be interposed between the inside of the porcelain tube and the center rest through the field adjustment. In addition it is difficult to externally confirm the status of the cushion after having been disposed on the inside of the porcelain tube. Thus problems have been raised in view of the quality and working of the center rest. Also there has been another disadvantage that the packing cost is expensive because the packing is strengthened upon the transportation.
Accordingly it is an object of the present invention to eliminate the disadvantage of the prior art practice as described above by the provision of a porcelain-clad electrical machine with a vibration-on-transportation suppression including additionally a simple means ensuring a resistance to excessive vibrations developed during the transportation thereof.